The PiJuice is the ultimate module for all portable Raspberry Pi projects. Includes many fun maker projects and a solar power version too! #ProjectPiJuice
Onboard 1400 mAh "off the shelf" Lipo battery (with support for larger Lipo Battery up to 5000 mAH+) to last up to 24 hrs + in constant use!
Full UPS (Uninterrupted Power Supply) solution.
Integrated RTC (Real Time Clock)
On board intelligent on/off switch
Low power deep-sleep state with wake on interrupt/calendar event
Programmable multi-colored RGB led
Full power management API available to Raspberry Pi OS with auto shutdown capability when running low on batteries
Raspberry Pi HAT compatible layout, with on board EEPROM for easy plug and play operation
Low profile design, to fit inside lots of existing Raspberry Pi cases!
PiJuice makes the Raspberry Pi an independent, stand alone platform. By using intelligent power behaviour, the integrated battery will keep itself topped up when plugged in, and supply any extra power needed to the Pi as required.
The real time clock on board will let your Pi know what time it is even with no power input or internet connection. It will also manage soft shut down and a true low power sleep state and intelligent start up from the off state.
You will be able to always keep track of the charge levels with the built in tri-coloured RGB LEDs, and since the PiJuice will use up to just five of your GPIO pins (just power and I2C), the rest are free to diversify your project even more. The stacking header allows you to continue to use your existing HATs and add ons with PiJuice.
The Robotics Inventors club is designed to put the power of inventing a robot to solve a real world problem in the hands of these elementary students and give them an early and accurate depiction of the ins and outs of the engineering design process from a unique perspective. The group has to develop their idea, organize it into manageable sections, build and test the individual sections, then integrate them together as a team and prepare to present and talk about their solution to the public.
This revolutionary concept is the result of the Infamous Robotics LLC Robotics Expansion programs that teach children about the STEAM (Science Technology Engineering Art and Math) fields using real robotics, not prepackaged kits. The robot the students build will amaze the world as it will show the capability of every child if we foster the inventor within them through our unique programs and courses.
How to get your child involved: The Robotics Inventors Club (RIC), created by Infamous Robotics LLC, is a unique and revolutionary concept that puts the power of inventing in the child’s hands. The RIC is only open to students of Infamous Robotics LLC summer camps, who have completed all introductory levels, Robotics Expansion 1-4. Mentoring is provided by the Infamous Robotics team.
Purpose: The purpose of this club is to formulate a unique group, a special group, unlike any being done at this age level. Members of the RIC will work as a team to engineer, design, test, build and ultimately present their robot during National Robotics Week in April.
The 2015 Robotics Inventors Club has chosen to build an autonomous robot to assist nurses with patients that have Ebola, called A.N.A. (Autonomous Nurse Assistant). The subsystem design and test is underway and the club members are planning on the prototype design to be completed soon.
At only 14 years old, Quin has started up his own KickStarter with his Qduino Mini: Arduino Compatible + Battery Charger & Monitor. Quin not only has the support of his parents, he is also being backed up by SparkFun Electronics. The Qduino Mini is perfect to embed in your electronics projects, it's super small, inexpensive, has a battery connector & charger built-in, & a fuel gauge that can tell you when to charge the battery!
The Qduino Mini is Arduino-compatible & 100% open source, hardware and software meaning that making and programming your first circuit is a breeze. Hardware is hard, so we decided to make it a little bit easier. The day that the first Qduino Mini ships, all of the design files, including EAGLE board files, schematic, and code will be released under an open source license. Here's what it includes:
Battery Charger Circuit - just plug in USB and it charges the battery with the auto switching circuit - there's no extra charger needed & no digging the battery out of your project so you can charge & program at the same time over USB!
Battery Fuel Gauge - guessing on when your project runs out of juice? We've got you covered - we have a simple monitor library for your battery so you can remind yourself when it needs a little extra juice.
Ultra small, Ultra thin, Ultra light - The Qduino Mini itself is 1in x 1.5in (2.6cm x 3.9cm) & 0.18oz (5 grams), perfect for quadcopters, drones or high altitude balloon projects. Both the Qduino Mini and the batteries (LiPos) used to power the board fit are super compact & thin, just right for embedding in your projects.
Starting out in electronics — as with any hobby — requires an investment of time, energy, and finances. This is especially true in the early stages, when unbridled enthusiasm blurs what expenditures on equipment and supplies are necessary and which are detours. It’s amazing how easy it is to succumb to the equipment acquisition disorder or EAD — even on a relatively tight budget.
EAD manifests itself in two ways. The first is in the number of pieces of equipment acquired — everything from a digital o’scope to a bench multimeter. The second is in the specifications of each piece of equipment, with a leaning towards an abundance of often unnecessary features.
For example, let’s say you start your adventure by setting up a workbench for microcontroller work. At the outset, you’ll be faced with determining what equipment is necessary, what’s nice to have, and what would simply add clutter to your workspace. If you’re like most novices, you’ll refer to advertisements, reviews, and perhaps join an online forum or two in hopes of determining exactly what you’ll need. Left to your own devices, you might accumulate a dozen different pieces of equipment — either new or used — as your budget allows.
Furthermore, you’ll be tempted to lean towards the feature-laden versions of each piece of equipment in the off chance that you might need those extra features one day — even though you’re unclear exactly what benefit you’ll derive from those features.
For example, let’s say you’re facing the choice of a $9 wall wart and a $300+ bench power supply. Even though the wall wart will probably be all you need for the first six months or so of your experimentation, you’ll be tempted to go for the bench supply. Then, there’s the issue of digital readout — number of digits, single readout for voltage and current, or dual digital readouts, currentlimiting features, and the like. You could easily end up with a power supply that not only requires more space on your bench, but that is so complex you’ll have to spend hours just learning to use every feature. Unless one of your goals is to master commercial power supplies, these are hours that you should have spent working directly with microcontrollers.
How do you avoid EAD? If you’re extremely lucky — or persistent — you’ll identify a mentor at a local electronics club who will take time to understand you, your plans, and real needs. The second best option is to identify a virtual mentor on one of the many online forums.
The challenge is finding a mentor that doesn’t have a hidden agenda linked to sales of equipment or supplies. Otherwise, you could end up with an even more severe case of EAD than if left on your own. I’ve found that the most credible online mentors emphasize ingenuity over equipment.
Another thing I’ve learned is that when exploring an unknown field, it’s better to learn one thing — be it a device or technique — thoroughly before moving on to something else. Taking this approach will naturally limit any EAD tendencies you might have.
Good luck experimenting. NV
An annual event in my old ham radio club was to hold a drawing for what began as a homebrew straight key gifted to a newcomer to the club. The original key — a momentary on switch — wasn't much more than a 3" copper bar, a thumb-tack contact, and a spring.
When the novice could afford a commercial key, he returned it to the original owner — with a few modifications. The improved key had a nice brass knob for the fingertips, and the flimsy base was replaced with a substantial slab of oak.
The key was passed on to the next needy club member in like fashion, with the expectation that it would be returned with some significant improvement. As I recall, by the fifth or sixth iteration of the gift/improvement process, the straight key had morphed into an iambic keyer with built-in sidetone oscillator.
That is, instead of pressing down on a fancy momentary open switch, the operator used the keyer by gently touching one pad with the thumb and the other pad with the index finger. Because finger motion was used instead of wrist and arm motion to operate the keyer, the result was much faster keying speeds.
Benefits of iambic keyers vs. straight keys aside, the point is that this little game of one-upmanship was one of the highpoints of the club. Everyone looked forward to their chance to demonstrate their prowess in circuit and mechanical design. It certainly was more entertaining — and challenging — than simply building a circuit according to a magazine article or duplicating a circuit developed by another club member.
In different issues of Nuts & Volts, you'll find articles that build on the work of others. In some ways, these can be considered a form of one-upmanship. In other ways, these articles are opportunities for you to demonstrate your ability to one-up previous writers. Sure, go ahead and build one of the projects. But don't stop there. See what you can do to improve on it — whether that involves making it simpler and more elegant, or adding a few new features.
Better yet, pass your handiwork off to a fellow experimenter and challenge them to one-up your work. In the end, everyone wins. NV
Nothing says "I Love You" more, than when it comes from the heart! This might just give you the inspiration you need if you just cant figure out what to get your significant other for valentines day. Do what we did in grade school, make something. Check out Henry's blog and see what he created from spare parts laying around.
Lemos International Co., Inc., of Barrington, RI and Merritt Island, FL has been appointed by ACKme Networks of Los Gatos, CA as its North American distributor and Value Added re-seller. ACKme offers fully certified small form factor Wi-Fi, Low Energy Bluetooth modules, and GSM Gateway solutions optimized for cellular sensor or command / Control applications.
Lemos has been a distributor for the high-end electronics industry since 1996, offering state-of-the-art technology. In 2011, Lemos International opened a facility in Merritt Island in order to better serve its customers as they design RF solutions for their products. Lemos commented that ACKme will fit perfectly into its current portfolio of high-end wireless products.
Welcome to the world of wireless know-how in the form of amateur or "ham" radio. Where else can you be an electronics and programming whiz, study solar and atmospheric phenomena, design your own communication system, and provide valuable public service — all at the same time? Amateur radio and the Nuts & Volts readership have a lot in common. Let's get to know each other!
I’m thrilled to help return ham radio to the pages of Nuts & Volts! In every other issue, I’ll be discussing some aspect of ham radio technology that you can use on your workbench and in your projects — whether you have (or get!) a license or not. Over the years, NV has featured ham radio in articles and columns so ham radio was never truly absent. The magazine’s editor is a ham (NU1N) and Paul Verhage — maven of the high altitudes and Near Space columnist — is also known as KD4STH. Many of the authors hold an amateur “ticket,” so maybe they will share their call signs with us in future articles. You may be surprised at how widespread amateur radio really is!
A little about my background: I have a degree in Electrical Engineering and spent 20 years in various types of industrial and medical product development — both hardware and software. I’ve had an amateur radio license since my high school days and am now known on the ham bands as NØAX (the slash is silent). For the last dozen years or so, I’ve been writing and editing books and columns for the American Radio Relay League (www.arrl.org), such as the three licensing study guides; a classic reference for radio technology, The ARRL Handbook; and a nearclassic antenna reference, The ARRL Antenna Book.
Some of my other books and columns are included in the sidebar on resources, including Ham Radio for Dummies. I’m pretty active on the air and like to operate in competitive events known as radiosport, as well as provide public service and study radio wave propagation. There is more on my “ham radio bucket list” than I will ever get to!
So, what is this ham radio stuff anyway and why should you care? First, there is far, far more to amateur radio in the 21st century than in the movies. Those images you see of glowing tubes and racks full of black crinkle-finish equipment with the jumping meters and dials? They are as obsolete as 8” singlesided floppy disk drives and 7400 family TTL logic! Sure, some of that gear is still out there on the air, but today’s ham radio is up to date and innovative.
Hams are big players in the Arduino and Raspberry Pi communities, just as they are in developing over-the-air digital communications protocols and networks. Even if you’re not really interested in the full ham radio experience, you might be interested in using non-licensed wireless data links in your projects, for example. Whatever your specialty, learning about radio will help you select, apply, and use wireless technologies better.
Modern-day ham radio is really a combination of three important components. The first is science: Hams learn about radio circuits and systems, antennas, how signals propagate from place to place, and the antennas that make it happen. The second is skill: By practicing effective operating, hams apply that science to insure that signals get from point A to point B. Finally, the ham combines the science and skill in service of his or her fellow citizens. You may have seen the motto “When All Else Fails,” which refers to the ham’s storied ability to fill in when commercial and government communications are disrupted.
All three aspects — science, skill, and service — are important, and there is a home for you in whichever area is most interesting.
This column will touch a lot of bases: antennas, transmission lines, batteries, digital protocols, radio frequency (RF) circuits and techniques, test equipment, and the list goes on. We’ll discover that components act a lot differently above a few megahertz (MHz) than they do at audio and DC. I will show you how to install those pesky feed line connectors so the signal goes to the right place.
Similarly, we’ll take a look at ways to keep RF signals from leaking out of and getting into your equipment. In some columns (like the one this month), there will be an experiment or activity you can do to gain valuable experience and maybe even a useful gadget. Ready to get started? I thought so!
The Ground Plane Antenna
There is no subject better suited to kick off a column about ham radio technology than antennas. All forms and specialties of ham radio share antennas as a common part of the station. If it’s ham radio, you can be sure of an antenna being involved. Actually, a lot of non-amateur electronics also deal with antennas, such as wireless links and mobile phones.
Figure 1. Basic ground plane construction showing the formula for the length of the vertical element and radials.At least two radials are required; four are recommended, and should be arranged symmetrically around the vertical element.
Figure 2. The quarter-wavelength long ground plane antenna behaves similarly to a half-wavelength long dipole antenna with two quarter wavelength halves. It uses a solid conductive sheet or radial wires to supply the same effect as that of the “missing” quarter-wavelength. In this column, I’ll introduce you to one of the simplest antennas and show you how to make one to use at home — or even design your own.
Figure 1 shows the basic idea: A vertical wire is attached to the center conductor of a coaxial cable connector, and several radial wires are attached to the mounting holes of the connector. This particular style of connector is called a receptacle or panel jack because it is designed to mount on a panel and have a cable attached to it. (Bulkhead receptacles mount with a nut and lock washer in a single hole, and won’t work for this particular antenna.)
A family of connectors shares common attachment mechanisms and body sizes. The receptacle we’re using here is from the BNC family. (Other common connector families include SMA, N, and UHF.)
The vertical wire — called an element — is the main part of the antenna that receives the signal. Does the orientation of the element matter? Yes, it does. Radio waves are made up of an electric or E field and a magnetic or H field that are at right angles to each other.
The magnetic field makes electrons move in tight little circles which is not very useful in creating currents that flow to a receiver. The electric field, however, makes electrons move in a straight line. In this case, the antenna is designed so the E field will make the electrons move back and forth along the wire element, into the coaxial cable, and down the cable to the receiver.
The orientation of the electric field determines the radio wave’s polarization — horizontal or vertical.
When the antenna element and radio wave E field are aligned, the antenna receives the strongest signal. The orientation of the antenna’s element or elements determines the antenna’s polarization. In this case, the antenna is vertically polarized. Since the NOAA Weather Station broadcasts that this antenna is designed to receive are transmitted by a vertically polarized antenna, our antenna should be vertically polarized to receive the maximum signal. (Misalignment is called crosspolarization and can result in up to 99% or 20 decibels [dB] of signal loss because the E field no longer makes electrons move along the antenna element as receivable current.)
An Electrical Mirror
The name “ground plane” comes from the four radial wires — so-called because they extend radially from the center. The ground plane acts as an electrical mirror to create an electrical image of the antenna’s missing half. Missing half? Yes, the ground plane antenna is actually one-half of a dipole as shown in Figure 2.
The mirroring effect of the ground plane is the same as that of the missing part of the dipole. In this case, four radials are enough to do the job. For ground plane antennas mounted on vehicles, the radials are replaced by the sheet metal of a roof or trunk.
A one-half wavelength long dipole is an effective antenna that radiates and receives equally well in all directions around the antenna’s axis. If the dipole is vertical, the equal response from any direction makes it omnidirectional.
That omnidirectional response is not repeated if one looks at the antenna’s response from the side. Figure 3A shows the ground plane’s elevation pattern starting at the horizon (0°) on one side, going over the top of the antenna (90°), and back to the opposite horizon. The antenna receives very little signal overhead because the E field of a radio wave coming from that direction only moves an electron back and forth across the element, not along the element where it becomes a current that can be received.
Figure 3A. These are radiation patterns showing how strongly an antenna responds to signals arriving from various directions.The distance from the center to the solid line shows the strength of the response in decibels with respect to the maximum response.This figure shows an elevation pattern looking at the antenna from the side.
Figure 3B. The threedimensional pattern resembling a bagel with the antenna at the center.The patterns were generated by the EZNEC antenna modeling software (www.eznec.com).
The notch in the antenna’s pattern is called a null, whereas the region of maximum response at the horizon is a lobe. An azimuth pattern would look down on the antenna from the top and show how well the antenna receives in all directions or azimuths. Since the antenna is omnidirectional, that pattern would be a simple circle.
Figure 3B shows what the antenna’s three-dimensional response looks like — sort of a bagel shape if the antenna was stuck through the middle.
By replacing the lower half of the dipole with its image, the quarterwave ground plane achieves the same effect of a vertical dipole, but in a smaller package with easier mounting. Ground plane antennas are common at frequencies from the AM and long-wave broadcast bands (at and below 1.7 MHz), all the way up to about 1 GHz wherever an omnidirectional response is desired.
A Ground Plane Antenna for NOAA Weather Stations
Many scanners and VHF radios have the ability to receive the seven NOAA weather station channels near 162.5 MHz (www.nws.noaa.gov/os/marine/wxradio.htm). The flexible whip (also known as “rubber duck”) antennas provided with portable radios are not very efficient. If you are in an area of weak coverage or are traveling to a remote area, you may need a full size antenna to pull in these stations. By building this simple ground plane antenna, you will be able to receive more of the stations over a wider area.
Parts List and Instructions
• Six foot BNC-to-BNC coaxial cable (RG-58 or RG-8X cable)
• BNC panel jack (UG-290 style or any flange-mount style)
• Eight feet of #14 AWG solid copper wire or brass rod (#12 to #16 will work and stand up to handling)
• Four ring crimp terminals for 12-16ga wire (blue insulation) for #4 stud
• #4 hardware to attach terminals to connector flange
Start by calculating the length of wire for the vertical element and the four radials. All five will be the same length. Use this equation with a frequency of 162.5 MHz:
L (inches) = 2772 / f (MHz) = 2772 / 162.5 = 17.1 inches
Where does the equation come from? Remember that the ground plane’s vertical element is one-quarter wavelength long or λ/4, where the Greek letter λ stands for wavelength. In free space at the speed of light, λ = 300 x 108 m/sec / frequency or λ/4 = 75 / frequency in MHz. Converting to inches, λ = 2798 / f (MHz). So, why are we using 2772 instead of 2798?
Figure 4. Close-up of the assembled ground plane showing one method of attaching radial wires to the BNC connector flange. Radials may be attached permanently by soldering, or temporarily with screws.
The speed at which a radio wave travels along a piece of wire is slower than in air or the vacuum of free space. That makes the wire act electrically longer than its physical length. In other words, λ/4 is shorter when the wave is traveling on a wire than it is when the wave is traveling in free space. The thicker the wire, the slower the wave travels. This is called the length-to-diameter (l/d) effect and it must be accounted for when determining the length of antenna elements. For #14 wire, the l/d effect results in the use of 2772 instead of the free space value of 2798.
Cut five pieces of wire. Crimp a terminal onto one end of four of the pieces. Solder the remaining piece of wire to the BNC receptacle’s center pin. Attach each radial to the receptacle with the #4 hardware.
Figure 4 shows one way to do it. Bend the radials down (away from the vertical element) about 45 degrees and arrange them symmetrically around the receptacle. Attach the coaxial cable to the antenna and the radio – you’re done! Figure 4 is a close-up of the antenna’s feed point where the feed line is attached. (If your radio uses some other type of
connector than BNC, you’ll need to use an adapter.) If your radio has a signal strength meter, compare your new antenna to the flexible antenna provided with your radio. Why are the radial wires bent at an angle when Figure 2 shows the ground plane as flat? If the radial wires (or conductive sheet) are at right angles to the vertical element, the feed point impedance of the ground plane will be about 35W which is different than that of the coaxial cable (which is usually 50W). This mismatch will make it harder for signals in the vertical element to transfer to the coax, and reduces the effectiveness of the antenna a bit.
By bending the radial wires down, the feed point impedance is raised closer to 50W. (Cable impedance will be the subject of a future column.)
Your antenna will perform well over a fairly wide range of frequencies that are up to ±5% from the design frequency. Table 1 shows the wire length for several commonly monitored radio services. Assuming you don’t want to hold the antenna up in the air with one hand when you want to use it, you can simply tape the supporting cable to a piece of dowel, pipe, conduit, or whatever is handy. Secure the support so the antenna is in the clear and at least l/2 away from any other metal surface or object.
I hope you’ve enjoyed this first installment of The Ham’s Wireless Workbench and will be a regular reader as we explore the world of ham radio technology. Visit the ARRL website and read what’s there — you’ll learn a lot and maybe I’ll eventually hear you on the air with your own call sign!
Until then, 73!
(That’s the ham’s shorthand for “best regards.”) NV
Radio and Radiation
The word “radiation” tends to get people excited because the same word is used to apply to all types of radiated energy — from radio waves to infrared light to X-rays and atomic particles. Radio waves as we are discussing here are non-ionizing, meaning they do not have enough energy to knock electrons away from atoms creating ions. The only effect from radio waves on humans is thermal or heating. For radiation to become ionizing, it takes extreme ultra-violet, X-rays, gamma rays, or particles to create ions and cause chemical changes in cells. For more information on safety issues associated with radio waves or RF, see http://www.arrl.org/rf-radiation-and-electromagnetic-field-safety
Where Does the Term “Ham” Come From?
Everybody wants to know why it’s called “ham” radio. While there are many answers floating around, the truth is that no one really has the definitive answer. Nevertheless, after being asked thousands of times, the most common and reasonable source of “ham” is that it was originally a not-very-complimentary term used to refer to the amateurs by commercial and military operators. In those days of spark transmission — the original ultra-wideband signal! — everybody had to share all of the radio spectrum, so interference was a huge problem. The amateurs turned the term into a badge of pride that persists to the present day. It’s not an abbreviation for anything, so it’s never capitalized. It’s referring to the original hackers — the hams.
Your Go-To Source for Radio Know-How – the ARRL
The world’s oldest amateur radio organization is also the United States’ national amateur radio institution: the American Radio Relay League, or the ARRL (http://www.arrl.org). Usually referred to by hams as “the League,” the ARRL’s motto is “Of, By, and For the Amateur.” It represents amateur radio internationally and in Washington, D.C. to insure that hams have the necessary spectrum to fulfill the amateur service’s role.
Within the amateur radio community — more than 700,000 in the United States alone — the ARRL’s role is to educate amateurs, support the volunteers who perform all licensing activities, and provide training and service activities to keep the skills of hams sharp and ready.
The ARRL publishes an enormous amount of technical and operating material in whatever area of amateur radio is most attractive to you. If you would like to explore some of the technology resources on the ARRL website, there is a special portal just for you at www.arrl.org/tech-portal.
Ham Radio for Dummies, Second Edition (Ward Silver NØAX) — An introduction to ham radio that explains what it is and how it works in bite-sized chunks.
ARRL Handbook — Now in its 92nd edition, “the Handbook” covers nearly all areas of amateur radio technology from tutorials in basic electronics to the latest digital protocols and equipment innovations. See the ARRL Store (http://www.arrl.org/shop/technical) for a long list of technical books.
Cleaning out my workshop reminded me of when I first started my journey in electronics — tubes were still available at RadioShack. My first ham radio transmitter — a HeathKit DX-60B — used a 6146B tube final amplifier (power amplifier), in part because it was inexpensive and readily available. Back then, I had a junkbox with a few dozen tubes, a pound or two of discrete resistors and capacitors, and some miscellaneous hardware. With that, I could repair just about any TV, receiver, or transmitter that I came across or wanted to modify.
Today, things are more complicated, in part because of the vast array of specialized solid-state components and assemblies available. Moreover, the shelf life of these components and assemblies are typically months instead of years or decades.
Don't get me wrong. I look forward to getting my hands on the latest developments in technology. I'm hooked, for example, on the new product announcements featured by SparkFun every Friday, and the broader daily updates on technology from Gizmodo. It's just that it no longer pays to have a sizeable junkbox.
For example, about a year ago, I created a prototype circuit for a government grant application that relied on some high-resolution TFT LCD modules from AdaFruit. However, in the nine months between the grant application and funding, the TFT LCD had been discontinued. As a result, I had to experiment with a new crop of LCDs and newly introduced OLEDs from AdaFruit. I was happy with the new displays, which provided higher resolution, faster response, and no increase in price. However, I had to modify the 3D printer file for the mounting assembly, and rework the software to accommodate the new generation of displays.
Today, after clearing out perhaps 20 lbs of retired ASICs (applicationspecific integrated circuits), breakout boards, and circuit assemblies, my junkbox consists largely of leaded and SMT resistors, capacitors, and a few 3V and 5V power regulator chips. I've downsized from six shelves of "junk" to one shelf of discrete components.
As a result, there's less to keep track of, and I know where everything is. Previously, it was a hunt to find that elusive chip or breakout board. Now, my hunting is reserved to online searches.
The two to three day time lag is a significant downside, but no greater than working with components that are no longer supported. So far, this “just in time” parts procurement has worked just fine.
As an aside, I've also shifted from what I once considered standard 4-40 stainless nuts and bolts from suppliers such as BoltDepot, to lighter smaller M2x10 hardware from places such as HobbyKing. I wouldn't think of building a drone or any other compact lightweight device with the old hardware.
However, there's still enough of the heavy duty boards around such as the Arduino UNO microcontroller board to hang on to my supply of 4-40 hardware. I'm sure that eventually — as with my collection of RF vacuum tubes — I'll be tossing these, as well. NV
When my friend,Vern asked me if I'd write an article for Nuts & Volts demonstrating how to create a Halloween decoration tombstone on a CNC router, I was psyched. I’m always looking for new and interesting ways to show off all you can do with CNC machines. So, I agreed to give it a shot.
Create complex 3D contoured parts by combining fast and simple 2.5D pocketing and profiling operations with manual finishing techniques.
As with any project, you have to do your research. I needed to answer questions like: What do tombstones look like? How are they shaped? What do they say on them? How are people using them in their Halloween displays? Most importantly: How do I make them on a CNC router? So, I got a lot of great design ideas examining epitaphs and tombstones using Google image search. Unfortunately, most of the models I found required 3D contouring. With that type of work, I would first need to spend the time creating a 3D model and even more hours carving it out.
There are three primary phases to a CNC project:
1) Design: The drawing or CAD model.
2) Tooling: Creating the tool paths with CAM software.
3) Machining: Running the tool paths on the machine.
I am admittedly an impatient man. With time being a finite resource we can never get back, isn’t everyone looking for a faster way? So, let me show you how you can use CNC routers to shortcut the 3D contouring process. First and foremost, you want to create your basic shapes and features using 2.5D operations. This is by far the biggest time saver. I’m talking about pocketing, profiling, and drilling mainly flat features on flat parts. You then follow it up with a bit of hand sculpting. This marriage between CNC and hand work produces impressive results for this type of project, while shaving valuable time from the process.
Figure 1. Cutting 2" foam stock
To start, I needed an inexpensive material that I could get from my local home improvement store that was easy to work with. The obvious choice was 2” thick foam insulation which I purchased in a 4 x 8 foot sheet for about $28. It’s thick enough to allow for a lot of depth and contrast in my design, which really pops when hit by a spot light on my lawn display. I happened to pick up a panel of pink Owens Corning — the one with the Pink Panther mascot (Figure 1). Other brands in other colors should work equally well.
I Think I CAM, I Think I CAM ...
My favorite piece of CAM software is Vectric’s VCarve Pro. This is by far the easiest-to-use CAM software on the planet. I also like how their software shows you a 3D preview of what the finished part will look like (Figure 2). I mention the CAM software first because the feature I like best is the built-in drawing tools, as opposed to other applications that require third-party drawing tools. This allows you to blend the first and second phases with a single piece of software.
Figure 2. 3D view of the tombstoned esign in VCarve Pro.
Given that, we will skip the first phase and blend it in to the second phase when we get to that point.
This article is not intended to be a step-by-step tutorial, so I will not go into the details of how to use VCarve Pro. There are plenty of excellent tutorials and sample projects on their website if you need help using any of their software. You can download the design files for this project at the article link or at www.probotix.com/downloads to help get you started or if you want to simply recreate my design.
The first step in the CAM software is to define your stock (length, width, and height) and also where you want the origin (the zero location) to be. You can choose the back right corner at the bottom of the stock, top dead center, front left corner, or the top of the stock — it’s wherever you need it to be. It can depend on a lot of things, but typically people use the front left corner at the top of the stock.
The next step is to import your drawing from another drawing program. In this case, you can take advantage of Vcarve’s built-in drawing tools to create your shapes. I design machines and electronics for a living, so mechanical design comes naturally to me. However, I really struggle with organic design. So, whenever I come across a project like this, I rely on a variety of resources to help me.
Design, Fonts, and Clipart
There are plenty of sources of clipart available online, but many of them are click farms in disguise, so beware. I really like the CD-ROM/DVD clipart collections that include categorized catalogs (long live print!). Most of these designs require a lot of cleanup before they can be machined. They were not designed for CNC and will often have both disconnected and hidden vectors that have to be reworked first. Boolean drawing tools are your friend here.
Another great source of simple shapes are themed dingbat fonts. They require very little work to make them machinable. The horned head in my design was one of the “letters” in such a font. Speaking of fonts, there are tons of free font websites out there where you can find a multitude of themed type styles for your designs.
Once you are satisfied with your design, you will assign tool paths to the various shapes in it. Vcarve has a variety of tool path operations, but for this project we are only using the pocketing and profiling operations. With any of the tool path operations, you will be assigning the tool geometry, starting depth, depth of cut, step-over, feed rate, plunge rate, direction of cut, and so on. Because I was working with foam, I was able to take some overly aggressive cuts.
The order of operations is important when laying out your tool paths. For instance, you may need to cut your shallower pockets first when you have overlapping or embedded pockets. If the stock is being held from the outer edges, the last operation should be to do your final outside profile pass. I didn’t have an end mill long enough to make it through the whole slab of 2” foam, so on my outside profile, I cut it through as far as I could, then hand cut the rest of the way through with a knife.
Now that you have your tool paths, you export them as g-code through the appropriate post-processor, and then carry that g-code over to the CNC machine on a USB thumb drive and load it into the control software. Our machines at Probotix run the open source software LinuxCNC.
I was cutting this particular part on the Probotix FireBall Comet™ CNC router that has a 25” x 25” work envelope (Figure 3). My foam slab was 18” x 24”, so I had to be careful that I mounted it to the table inside of the travel envelope of the machine. Double-sided 3M tape that has the green argyle backing is what I like to use for mounting stock to my table. Use a generous amount so the stock doesn’t come loose in the middle of the job.
Figure 3. Probotix Fireball Comet CNC Router.
Figure 4. Screenshot of LinuxCNC showing tool paths.
Once the stock is mounted, install the tool into the spindle and then jog the tool over to the corner that you chose for the origin in the CAM software. Then, you will “touch off” each axis. What you are doing is telling the control software that you are now sitting at the starting point of each axis, or X0 Y0 Z0.
Give yourself a sanity check and look at the 3D toolpath on the display. You want to make sure that the tool path appears where you think it should within the work envelope bounding box on the screen (Figure 4). Then, hit the start button, sit back, and watch (Figure 5).
About 30 minutes later, you will have the basic tombstone carved out. So, pry it off the table and remove the double-sided tape. Figure 6 shows what it looked like after I cut off the outside scrap. Pretty cool already, but not very scary looking ... yet.
Figure 5. Fireball Comet in action - cutting the tombstone design.
Figure 6. Tombstone after maching, but before handwork and paint.
The next step is to hand contour the piece to rough it up so it looks aged and weathered. There are many tools and methods you could use here, and you could spend a lot of time adding detail. Remember how impatient I am, though? I grabbed a die grinder with a rasp bit and a sanding wheel. I also used a hand rasp, and then smoothed out certain parts of the tombstone with some DAP fast drying latex caulk (Figure 7). Watch out for that die grinder — you can remove too much material in a hurry if you are not careful.
Figure 7. Die grinder, hand file, sand disc, and caulk.
So far, so good, but have you ever seen a pink tombstone? Me neither. So, let’s change its color!
I love modern spray paint technology. There are many fast-drying exotic finishes available — your options are limitless. You can get a fantastic finish with little time and effort. A fleck stone spray paint finish was very tempting here, but since most spray paints will dissolve foam, I decided to use latex. I chose a satin gray as my base coat, and then used gray, black, and burnt umber mixes to weather and shade the tombstone (Figure 8).
Figure 8. Painting supplies and brushes.
Save Time, Save Money
You can spend a little time or a lot of time here. These tombstones are typically viewed under low light conditions, so I was looking mostly for contrast and depth, and that didn’t require a lot of time. Here is a breakdown of the time invested in this project:
Research: 3 hours
Design time: 1 hour
CNC routing: 30 minutes
Hand contouring: 10 minutes
Painting: 30 minutes
So, my total time was 5:10.
Compare that to the 10-20 hours that could easily be spent on a full CNC 3D contouring to accomplish the same thing (Figure 9)!
Figure 9. Finished tombstone decoration.
All-in-all, I was pretty satisfied with the results from such a small investment in time. If I were going to do this again, I would have spent more time and creativity on the tombstone verbiage.
Do a Google search for “funny epitaphs” to get some inspiration. Maybe include names of family members or friends. Add an Arduino and LED lights. Then, make a whole graveyard full of them if you want!
Most importantly, make sure to work safe and have fun! NV
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